Reply
 
Thread Tools Search this Thread Display Modes
 
Old 11-19-2005, 08:27 PM   #15
Rivet Master
 
RichardT's Avatar
 
Join Date: Sep 2003
Posts: 925
Quote:
Originally Posted by 59toaster
U b a smart feller.....
What if you switched the "sm" and the "f"
__________________

__________________
RichardT is offline   Reply With Quote
Old 11-19-2005, 08:30 PM   #16
Rivet Master
 
59toaster's Avatar
 
1959 22' Caravanner
Atlanta , Georgia
Join Date: Feb 2003
Posts: 2,197
Images: 22
Quote:
Originally Posted by RichardT
What if you switched the "sm" and the "f"
He would have to chang his nick to "stinky" then.
__________________

__________________
1959 22' Caravanner
1988 R20 454 Suburban.
Atlanta, GA
59toaster is offline   Reply With Quote
Old 11-19-2005, 09:09 PM   #17
_
 
. , .
Join Date: Dec 2004
Posts: 8,812
hi nick and others

this is a good effort and explanation of what load bars do and how much (proportional weight) force is required to redistribute tongue weight... redistributing tongue load takes less bar deflection with short trucks and trailers....right?

you must me in mathematics nick?

it always gets "deep" when words are combined with math forumla...i've always thought graphics with math made for better understanding.

my background is medicine, so i only understand enough math and physics to kill folks...

now for a couple of issues/questions....i agree the trailer can function like a simple seesaw (single fulcrum lever) but the truck? wouldn't we need to know the center of gravity/balance point for the truck? most of the diesel rigs are very front heavy...until we get the beds loaded up....but still seems we'd need to know cog instead of just the overhand?

next the load bars are steel with a stiffness/deflection/elasticity that isn't linear...what i'm trying to say is that as the bars bend the force needed to bend them changes....although your example does focus on lbs of force not inches of flex...but as the bars flex the 'effectiveness' of their force transfer changes...? increasing force from 1000 to 1400 doesn't really move 1/3 more does it?

and wouldn't you really need an inline tensiometer on the chains/worm drives to measure the lbs of force generated in the load bars?

so would i use a spreadsheet to set up my rig....not at this point. i think there are too many variables not accounted for, for the math to be accurate....the cat scales would still seem a better method.

lastly...even if you finesse the math some this still doesn't help those folks trying to understand inland andy's issue of shaking the trailers (and nick isn't trying to explain this)...........

inland andy's concept of light bars on stiff trucks.... is really about trying to decrease transmission of high frequency/low amplitude vibration....i think.

cheers
2air'
__________________
2airishuman is offline   Reply With Quote
Old 11-19-2005, 10:14 PM   #18
Rivet Master
 
fastrob's Avatar
 
1976 25' Tradewind
. , AZ to Maine
Join Date: Sep 2004
Posts: 545
Keep It Simple

Very nice thought chain. Good work. Thanks for sharing.

I called the manufacturer and asked enough questions until satisfied about the answers for our setup.

But there is more to it than this; nothing can compensate for an incompetent driver. Happy Trails.
__________________
fastrob is offline   Reply With Quote
Old 11-19-2005, 11:08 PM   #19
Rivet Master<br><img src="/ugala/forums/images/5rivet.gif">
 
CanoeStream's Avatar

 
2006 25' Safari FB SE
St. Cloud , Minnesota
Join Date: Aug 2003
Posts: 13,279
Images: 19
Blog Entries: 3
Rivet The "why" works for me...

C'mon y'all -- if you hadn't been dear hunting last weekend you'd have seen this post that probably was the final stimulus to get Nick thinking: http://www.airforums.com/forum...rty-19133.html

What we really need is more dialog at the level 59toaster & 2airishuman are suggesting. It's not easy to understand but there are some tough choices to analyze. Nick, I'm following so far. Thanks!
__________________
Bob

5 meter Langford Nahanni

CanoeStream is offline   Reply With Quote
Old 11-20-2005, 07:34 AM   #20
Moderator Emeritus
 
Pick's Avatar
 
1972 31' Sovereign
High Springs , Florida
Join Date: May 2002
Posts: 2,310
Images: 36
Send a message via AIM to Pick
Loved that post Nick. What would really be interesting, is if we could find some electronic tension sensors, similar to what they use to convert old beam scales to electronic scales. Replace a link in each chain with the sensors, and actually measure the tension. Then drive down the road and watch the chain tension change. Of course we would have to have a laptop recording and graphing all this........
__________________
ARS WA8ZYT
2003 GMC 2500HD 4X4 D/A Ext. Cab
Propane Powered Honda EU2000i
Lots of Hot Sauce!
Air # 283
WBCCI 1350
Pick is offline   Reply With Quote
Old 11-20-2005, 09:48 AM   #21
Rivet Master
 
Join Date: Dec 2002
Posts: 1,313
Images: 4
To respond to some of the comments so far:
Markdoane said
If someone would enter the spring rates (lbs/in deflection) for the various weight bars, we could combine this with Inland Andy's recommendation for 1-2 inch bend and tell exactly which bars to order.”

Yes, exactly so, and a great idea. The equations are simple practical tools to assist in the selection of a load distribution hitch. An analogy would be the decision as to which paddle a kayaker should buy. The vendor should give advice based on the height of the paddler, the beam of the kayak, the type of water being traveled. The kayaker should then be equipped with a paddle “fit for purpose”. However, it doesn’t mean she’ll be safe or efficient in the real world situation of moving water. That will require skill, experience and judgment. Just like towing heavy.

59 toaster said
“That will once and for all put it to rest what bars with how much deflection is needed to make a DC work properly in an emergency situation and back up Inland Andy's observations about "over hitched".

My guess (and it’s no more than that, so not very helpful), is that although a certain bar tension is required for a given rig for correct load distribution, this tension could be obtained from either:
(a) A stiff bar with a small deflection, OR
(b) A soft bar with a larger deflection.

I guess that the soft bar with the larger deflection would be far preferable when the rig is traveling. When traveling over bumps, the load distribution effect would remain steadier, as a one inch deflection of the soft bars would have less impact on this effect and hence the trailer behavior would be more stable. Also, the impact loads on the trailer would be lessened, and thus cause less stress on the trailer. (Andy’s point, I believe). As 59 toaster said, this will enable more consistent sway control from the Dual Cam hitches.

2Air makes some very good points
....i agree the trailer can function like a simple seesaw (single fulcrum lever) but the truck? wouldn't we need to know the center of gravity/balance point for the truck? most of the diesel rigs are very front heavy...until we get the beds loaded up....but still seems we'd need to know cog instead of just the overhang?”

2Air has hit on the central difficulty in analyzing this issue. In the real world, the center of rotation of the TV will depend on the relative hardness of the front and rear springs. In the past I have attempted to include these variables, but the math became too complex to be of practical use to me. By assuming the suspension is rigid, I have attempted to produce a practical, usable, set of equations whose accuracy is sufficient for the purpose. By concentrating on returning the TV front axle to its original height, I have attempted to minimize the distortion caused by the assumption.

“increasing force from 1000 to 1400 doesn't really move 1/3 more does it?”

Yes, I believe so. As you correctly state, I have concentrated on the tension in the chains, and not the required deflection of the bars. The sophisticated way to find out is by following Pick’s excellent suggestion!

I have to take my 4 year old granddaughter (number 5) out into the woods to show her how to break trail, mark trail etc, so farewell for now.
Nick.
__________________
Nick Crowhurst, Excella 25 1988, Dodge Ram 2500 Cummins Diesel. England in summer, USA in winter.
"The price of freedom is eternal maintenance."
nickcrowhurst is offline   Reply With Quote
Old 11-20-2005, 12:44 PM   #22
Round on both ends
 
SafeHarbor's Avatar
 
1979 31' Excella 500
1975 28' Argosy 28
Rutledge , Georgia
Join Date: Apr 2005
Posts: 783
Images: 39
What I'm very happy about is that I also have an Excella 31 and a 3/4 ton Dodge diesel. Now that Nick's done the thinking... I'll just get whatever lift bars he gets.

Lamar
__________________
1975 Argosy 28 "Argosy"
1979 Excella 500 31 "Betsy"
1992 Lincoln Mk 7 LSC
2003 Dodge 2500 Cummins "TowHog"
"Lucy Loosehair" the cat - Airstream mascot
Klaatu barada nikto
SafeHarbor is offline   Reply With Quote
Old 11-20-2005, 01:46 PM   #23
Rivet Master
 
Join Date: Dec 2002
Posts: 1,313
Images: 4
Lamar, I've just entered your figures into the equation, assuming your empty tongue weight of 580 pounds, 33 inch bars, and 206 inches (a guess) from trailer axle center to ball, and rear TV overhang of 60 inches. The chain tension required is 816 pounds, or 408 pounds per chain. That's about 20% less than my rig, because of your lower tongue weight I obtained from searching this forum. I use an Eaz-lift 1000lb hitch!
Nick.
__________________
Nick Crowhurst, Excella 25 1988, Dodge Ram 2500 Cummins Diesel. England in summer, USA in winter.
"The price of freedom is eternal maintenance."
nickcrowhurst is offline   Reply With Quote
Old 11-20-2005, 02:07 PM   #24
Round on both ends
 
SafeHarbor's Avatar
 
1979 31' Excella 500
1975 28' Argosy 28
Rutledge , Georgia
Join Date: Apr 2005
Posts: 783
Images: 39
Thanks, Nick!

I've just read the thread from last year that contains lots of good information from Inland Andy and others, and my fuzziness on this is clearing up somewhat.

The purpose of using the lighter weight lift bars is to acheive more deflection and springiness (boingo-boingo) in the lift bars while maintaining enough force to keep the bolt-on (in my case) cams seated in straight-ahead motion, bumpy motion, and stopping motion. This seating pressure is also essential to maintaining the antisway properties.

A too-heavy set of lift bars does not have enough springiness, so the shearing forces transmitted to the front end of the trailer eventually beat the trailer to death.

But... here's where I'm still fuzzy. Can the 550 lb lift bars distribute more than 550 lbs tounge weight to the TV and AS? Since there are two of them, does that mean they can distribute 550 lbs x 2? (See, I'm capable of making my OWN head hurt.)

Remember that started me out with all of this are the 1,000 lb lift-bars I have that worked GREAT on my Dakota.

Lamar
__________________
1975 Argosy 28 "Argosy"
1979 Excella 500 31 "Betsy"
1992 Lincoln Mk 7 LSC
2003 Dodge 2500 Cummins "TowHog"
"Lucy Loosehair" the cat - Airstream mascot
Klaatu barada nikto
SafeHarbor is offline   Reply With Quote
Old 11-20-2005, 02:29 PM   #25
Rivet Master
 
Join Date: Dec 2002
Posts: 1,313
Images: 4
Quote:
Originally Posted by SafeHarbor
Can the 550 lb lift bars distribute more than 550 lbs tounge weight to the TV and AS? Since there are two of them, does that mean they can distribute 550 lbs x 2?Lamar
Only the manufacturer can explain what is meant by their ratings. The Eaz-Lift website describes a 1000 pound hitch as being able to redistribute a 1000 pound tongue weight. This is, at best, a simplification based on the "average TV rear overhang" and " average hitch to trailer axle center distance". Certainly, the chain tension is doubled if two chains are under equal tension.To answer your previous point, from equation 8,
D= (T*H*L)/(B*(H+L)) hence
D/T=(H*L)/(B*(H+L)) This shows that a total chain tension can distribute a tongue load greater than that chain tension, if (B*(H+L) is greater than (H*L).
Nick.
__________________
Nick Crowhurst, Excella 25 1988, Dodge Ram 2500 Cummins Diesel. England in summer, USA in winter.
"The price of freedom is eternal maintenance."
nickcrowhurst is offline   Reply With Quote
Old 11-21-2005, 06:12 AM   #26
3 Rivet Member
 
the ponz's Avatar
 
Detroit , Michigan
Join Date: Oct 2003
Posts: 150
Images: 6
adding momentum

Please recalculate using the following additional variables:


40,000# tractor trailer...



applied to the rear bumber.



BarkingSpider, did you replace the hitch along with the trailer?
__________________
86' 31' Sovereign
the ponz is offline   Reply With Quote
Old 11-21-2005, 07:50 AM   #27
Aluminut
 
Silvertwinkie's Avatar
 
2004 25' Safari
. , Illinois
Join Date: Feb 2003
Posts: 10,334
Quote:
Originally Posted by the ponz
It would seem to me that there must be an easier way for one to get to 500 posts

Nick, even though you lost me mid way, I love the fact that you've thought this that far through.

As for what ponz said about easier ways to get to 500 posts, heck, you should see some the post I have that took to get to 4600 and change this one had far more substance (and assumptions too)!
__________________
Silvertwinkie is offline   Reply With Quote
Old 11-21-2005, 08:17 AM   #28
Rivet Master
 
Join Date: Dec 2002
Posts: 1,313
Images: 4
Quote:
Originally Posted by Silvertwinkie
Nick, even though you lost me mid way, I love the fact that you've thought this that far through.
Twink, thank you for the kind encouragement. If I've lost you, that's a failing in my explanation.
Nick.
__________________

__________________
Nick Crowhurst, Excella 25 1988, Dodge Ram 2500 Cummins Diesel. England in summer, USA in winter.
"The price of freedom is eternal maintenance."
nickcrowhurst is offline   Reply With Quote
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Hitches and your dealer.... luckydc Hitches, Couplers & Balls 0 04-19-2004 08:34 AM
Electr. Tongue Jack Wiring?? roessler Jacks, Stabilizers, Lifting and Leveling 12 07-17-2002 12:00 PM
Replacing Black Water Tank Tamara Waste Systems, Tanks & Totes 15 06-18-2002 11:45 PM
Need spring load clips for water heater door 68 GT. Jim Clark Water Heaters, Filters & Pumps 4 05-09-2002 08:39 AM
Towing a small 60s trailer with a SUV... Andy R Tow Vehicles 15 03-30-2002 08:57 PM


Virginia Campgrounds

Reviews provided by




Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -6. The time now is 07:35 PM.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.

Airstream is a registered trademark of Airstream Inc. All rights reserved. Airstream trademark used under license to Social Knowledge LLC.